Conda

New Features
* constrained, optional dependencies (4982)
* conda shell function (5044, 5141, 5162, 5169, 5182)
* resolve 5160 conda xontrib plugin (5157)
* resolve 1543 add support and tests for --no-deps and --only-deps (5265)

Deprecations/Breaking Changes
* remove support for with_features_depends (5191)

Improvements
* filter out unwritable package caches from conda clean command (4620)
* envs_manager, requested spec history, declarative solve, and private env tests (4676, 5114, 5094, 5145)
* make python entry point format match pip entry points (5010)
* resolve 5113 clean up CLI imports to improve process startup time (4799)
* resolve 5121 add features/track_features support for MatchSpec (5054)
* resolve 4671 hold verify backoff count in transaction context (5122)
* resolve 5078 record package metadata after tarball extraction (5148)
* resolve 3580 support stacking environments (5159)
* resolve 3763, 4378 allow pip requirements.txt syntax in environment files (3969)
* resolve 5147 add 'config files' to conda info (5269)
* use --format=json to parse list of pip packages (5205)

Bug Fixes
* fix some conda-build compatibility issues (5089)
* resolve 5123 export toposort (5124)
* fix 5132 signal handler can only be used in main thread (5133)
* fix orphaned --clobber parser arg (5188)
* fix 3814 don't remove directory that's not a conda environment (5204)
* fix 4468 _license stack trace (5206)
* fix 4987 conda update --all no longer displays full list of packages (5228)
* fix 3489 don't error on remove --all if environment doesn't exist (5231)
* fix 1509 bash doesn't need full path for pre/post link/unlink scripts on unix (5252)

Non-User-Facing Changes
* eliminate index modification in Resolve.__init__ (4333)
* new MatchSpec implementation (4158)
* update conda.recipe for 4.4 (5086)
* resolve 5118 organization and cleanup for 4.4 release (5115)
* remove unused disk space check instructions (5167)
* localfs adapter tests (5181)
* extra config command tests (5185)
* add coverage for confirm (5203)
* clean up FileNotFoundError and DirectoryNotFoundError (5237)

Improvements
* resolve 3689 better error messaging for missing anaconda-client (5276)
* resolve 4795 conda env export lacks -p flag (5275)

Bug Fixes
* fix 5272 conda env export ugliness under python2 (5273)
* fix 4596 warning message from pip on conda env export (5274)

Improvements
* resolve 4224 warn when pysocks isn't installed (5226)
* resolve 5229 add --insecure flag to skip ssl verification (5230)
* resolve 4151 add admin indicator to conda info on windows (5241)

Bug Fixes
* fix 5152 conda info spacing (5166)
* fix --use-index-cache actually hitting the index cache (5134)
* backport LinkPathAction verify from 4.4 (5171)
* fix 5184 stack trace on invalid map configuration parameter (5186)
* fix 5189 stack trace on invalid sequence config param (5192)
* add support for the linux-aarch64 platform (5190)
* fix repodata fetch with the `--offline` flag (5146)
* fix 1773 conda remove spell checking (5176)
* fix 3470 reduce excessive error messages (5195)
* fix 1597 make extra sure --dry-run doesn't take any actions (5201)
* fix 3470 extra newlines around exceptions (5200)
* fix 5214 install messages for 'nothing_to_do' case (5216)
* fix 598 stack trace for condarc write permission denied (5232)
* fix 4960 extra information when exception can't be displayed (5236)
* fix 4974 no matching dist in linked data for prefix (5239)
* fix 5258 give correct element types for conda config --describe (5259)
* fix 4911 separate shutil.copy2 into copy and copystat (5261)

Non-User-Facing Changes
* resolve 5138 add test of rm_rf of symlinked files (4373)
* resolve 4516 add extra trace-level logging (5249, 5250)
* add tests for --update-deps flag (5264)

Improvements
* fall back to copy if hardlink fails (5002)
* add timestamp metadata for tiebreaking conda-build 3 hashed packages (5018)
* resolve 5034 add subdirs configuration parameter (5030)
* resolve 5081 make pinned packages optional/constrained dependencies (5088)
* resolve 5108 improve behavior and add tests for spaces in paths (4786)

Bug Fixes
* quote prefix paths for locations with spaces (5009)
* remove binstar logger configuration overrides (4989)
* fix 4969 error in DirectoryNotFoundError (4990)
* fix 4998 pinned string format (5011)
* fix 5039 collecting main_info shouldn't fail on requests import (5090)
* fix 5055 improve bad token message for anaconda.org (5091)
* fix 5033 only re-register valid signal handlers (5092)
* fix 5028 imports in main_list (5093)
* fix 5073 allow client_ssl_cert{_key} to be of type None (5096)
* fix 4671 backoff for package validate race condition (5098)
* fix 5022 gnu_get_libc_version => linux_get_libc_version (5099)
* fix 4849 package name match bug (5103)
* fixes 5102 allow proxy_servers to be of type None (5107)
* fix 5111 incorrect typify for str + NoneType (5112)

Non-User-Facing Changes
* resolve 5012 remove CondaRuntimeError and RuntimeError (4818)
* full audit ensuring relative import paths within project (5090)
* resolve 5116 refactor conda/cli/activate.py to help menuinst (4406)

Improvements
* additions to configuration SEARCH_PATH to improve consistency (4966)
* add 'conda config --describe' and extra config documentation (4913)
* enable packaging pinning in condarc using pinned_packages config parameter
as beta feature (4921, 4964)

Bug Fixes
* fix 4914 handle directory creation on top of file paths (4922)
* fix 3982 issue with CONDA_ENV and using powerline (4925)
* fix 2611 update instructions on how to source conda.fish (4924)
* fix 4860 missing information on package not found error (4935)
* fix 4944 command not found error error (4963)

Improvements
* allow pkgs_dirs to be configured using `conda config` (4895)

Bug Fixes
* remove incorrect elision of delete_prefix_from_linked_data() (4814)
* fix envs_dirs order for read-only root prefix (4821)
* fix break-point in conda clean (4801)
* fix long shebangs when creating entry points (4828)
* fix spelling and typos (4868, 4869)
* fix 4840 TypeError reduce() of empty sequence with no initial value (4843)
* fix zos subdir (4875)
* fix exceptions triggered during activate (4873)